Die NMR-Spektren von CF3I,CF3IF2 und CF3IF4

The NMR Spectra of CF₃I, CF₃IF₂, and CF₃IF₄ The ¹⁹F-NMR and ¹³C-NMR spectra of CF₃I, CF₃IF₂ and CF₃IF₄ were recorded in acetonitrile solution. The chemical shifts of the CF₃-groups are strongly dependent on the oxidation state of the iodine atom. With increasing oxidation state the resonances of the CF₃-groups in the ¹⁹F-NMR spectra are characteristically shifted to high field, whereas in the ¹³C-NMR spectra a characteristic shift to low field is measured. The absolute value of the coupling constants ¹J(¹⁹F? ¹³C) increases with increasing oxidation state from 344 Hz (CF₃I) via 354 Hz (CF₃IF₂) to 359 Hz (CF₃IF₄).     

Some perfluorocarbocyclic ethers and polyethers from hexafluorobenzene

High-resolution nuclear magnetic resonance (NMR) spectroscopy was used to determine the microstructures of some perfluorocarbocyclic ethers and polymers from reactions of bis(fluoroxy)-difluoromethane and hexafluorobenzene. The thermal and photochemical reactions of CF₂(OF)₂ and excess hexafluorobenzene are described. The structures of several new perfluoro-1,3-dioxolanes in which the rings constituted part of a bicyclic system were elucidated by ¹⁹F-NMR, gas chromatograph, gas chromatograph-infrared, and gas chromatograph-mass spectra. The copolymers of molecular weight about 2500 are, with 40% of the difluoromethylenedioxy groups, estimated by ¹⁹F-NMR to be in the polymer chain and the rest as pendant groups to the perfluorocyclohexylene and perfluorocyclohexenylene moieties. The suggested polymer structures are described and the mechanisms discussed.     

Cationic ring-opening polymerization of oxetane derivatives initiated by superacids: Studies on their propagating mechanism and species by means of 19F-NMR

The nature of ring-opening polymerization of oxetane derivatives initiated by triflic acid and triflic anhydride was investigated via ¹⁹F-NMR spectroscopy. Two types of propagating species, which were directly observed from the ¹⁹F-NMR spectra, were found to be oxonium macroions and triflic macroesters. These two propagating species established and equilibrium relationship during the polymerization process. The forming of oxonium macroion active species was highly dependent upon the substituents of the oxetane ring, and were enhanced when a more polar solvent was employed. The initiator effect, which occurred primarily in the initiating stage of the polymerization, is also discussed. © 1994 John Wiley & Sons, Inc.     

Synthesis and properties of sulfur cyanide trifluoride,SF3CN,sulfur dicyanide difluoride,SF2(CN)2, and sulfinyl cyanide fluoride,FS(O)CN

Sulfur cyanide trifluoride, SF₃CN, and sulfur dicyanide difluoride, SF₂(CN)₂, have been prepared by metathesis between sulfur tetrafluoride, SF₄, and trimethyl silyl cyanide, (CH₃)₃SiCN, at – 30°C. Treatment of SF₃CN with freshly sublimed selenium dioxide, SeO₂, lead to sulfinyl cyanide fluoride, FS(O)CN. IR, Raman, ¹⁹F-NMR, uv and mass spectra of the novel compounds are presented as well as some physical and chemical properties.     

Die Pentafluoro-orthoselen- und -orthotellurgruppe,eine 19F-Kernresonanzuntersuchung

A ¹⁹F-NMR Study of the (Pentafluoro)orthoselenium and -tellurium Group In ¹⁹F-nmr the (pentafluoro)orthoselenium and (pentafluoro)orthotellurium groups show characteristic AB₄ spectra. Chemical shifts give information about the different bondings. The axial fluori ne atom is often more influenced, a certain trans effect may be discussed. The values of is otopic splittings, coming from ⁷⁷Se agree with these observations, isotopic splittings from ¹²³Te und ¹²⁵Te are much less important. Comparison is done with selected compounds containing a (pentafluoro)orthosulphur group.     

Short branching in poly(vinyl alcohol). II. NMR spectroscopy of model polymers of short-branched poly(vinyl alcohol)

In order to develop a method of measuring the amounts of short branches in PVA, an NMR study was made of a model poly(vinyl alcohol) having short branches, one or two monomer units in length. Detection and estimation of the short branches were shown to be possible by using the ¹³C-NMR spectra of PVA and the ¹H-NMR of acetylated PVA. In the ¹⁹F-NMR spectra of trifluoroacetylated model PVA, the resonance peaks of primary and tertiary alcohols in the branching structure were not well resolved from that of secondary alcohol of the main chain.     

Nucleophilic displacement in polyhalogenoaromatic compounds. Part X. Transmission of substituent effects in polyfluorobiphenyl derivatives

The rate of methoxydefluorination (NaOMe-MeOH, 323.2 K) and the ¹⁹F-NMR chemical shifts of some substituted penta- and nona-fluorobiphenyls have been measured. The observed substituent effects parallel those found in the corresponding pentafluorobenzenes and demonstrate proportionate transmission of the total substituent electronic effect across the aromatic system.     

Umsetzung von Metall- und Metalloidverbindungen mit mehrfunktionellen Molekülen, 8. Mitt.

N-substituted halogenoacetamides react with halogenoboranes to the title compounds. The corresponding N-substituted halogenoimines result as byproducts. The importance of inductive and steric effects of the substituents is shown by the fact, that certain N-substituted halogenoacetamides react under formation of N-substituted halogenoimines only.¹H-,¹¹B-, and¹⁹F-NMR spectra, mass spectra and characteristic IR group frequencies are reported.

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7. Mitt.:W. Maringgele undA. Meller, Mh. Chem.108, 751 (1977).     

Darstellung und Untersuchung von Aminoschwefeltrifluoriden sowie eines Hydrolyseprodukts, 1-(Fluorooxothio)-2,5-dihydropyrrol

Synthesis and Investigation of Aminosulphur Trifluorides and of a Hydrolysis Product 1-(Fluorooxothio)-2,5-dihydropyrrole The reaction of previously unknown (trimethylsilyl)amines with sulphur tetrafluoride gives some new aminosulphurtrifluorides. Experiments to cleaver 1-(Trifluorothio)-2,5-dihydropyrrole and 1-(trifluorothio)pyrrolidin into butadiene and ethylene respectively and NSF₃ by way of a chelotrope cycloelimination were unsuccessful. ¹H-NMR and ¹⁹F-NMR spectra revealed the nitrogen in the aminosulphur trifluorides must be regarded sp³ hybridized rather than sp².     

Analyse von Hydroxysteroiden mit Hilfe der19F-NMR-Spektroskopie

Zusammenfassung Fluorresonanzsignale zeigen Änderungen der chemischen Umgebung eines Fluorkerns wesentlich empfindlicher an als Protonenresonanzsignale. Die chemischen Verschiebungen der CF₃-Singuletts trifluoracetylierter Hydroxylgruppen am Steroidgerüst sind in charakteristischer Weise von Position und Konfiguration der OH-Gruppen abhängig. Daher können Hydroxylgruppen an den C-Atomen 3, 6, 11, 12, 17 und in der Seitenkette an Ring D von Steroiden einfach und schnell mit Hilfe der¹⁹F-NMR-Spektren der Trifluoracetylderivate charakterisiert werden. Diese empfindliche Sensortechnik erlaubt Strukturbestimmungen und quantitative Analysen von Hydroxysteroidgemischen im Mikrogrammbereich.

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Analysis of hydroxy steroids by¹⁹F-NMR spectroscopyDetermination of structure and quantitative analyses of hydroxy steroid mixtures in the microgram range

Compared with proton resonance signals fluorine resonance signals depend much stronger on differences in the chemical environment of a fluorine nucleus. The¹⁹F-NMR shifts of the CF₃ singlets of trifluoroacetylated hydroxy groups on the steroidal skeleton characteristically reflect the position and configuration of OH groups on the carbons 3, 6, 11, 12, 17 and on the side chain at ring D. Therefore this sensitive technique provides a convenient tool for the structure elucidation and for quantitative analysis of mixtures of hydroxy steroids in the microgram range.

     

Chemistry of trifluorostyrenes and their dimers: 2. Synthesis of substituted α, β, β-trifluorostyrenes and α, β, β-trifluoroethenylnaphthalenes. Hammett correlations of their NMR parameters and the concept of “distorted π-electron clouds”

Six α, β, β-trifluorostyrenes with the following substituents, viz., p-MeO, p-Me, m-Me, p-Cl, m-Cl, and m-CF₃, were synthesized by the reaction of the corresponding Grignard reagents with tetrafluoroethylene in tetrahydrofuran. Similarly, α-and β-trifluoroethenylnaphthalenes were prepared. The substituent electronic effects on the ¹⁹F-NMR parameters were investigated for the trifluorostyrenes (I). Linear correlations between the Hammett σ constants and the following ¹⁹F-NMR parameters were established, namely, chemical shifts δ. (F¹) and δ (F²), coupling constants J₁₂, differences of chemical shifts Δδ_3-1 (δ (F³)—δ(f¹) or Δδ_3-2. The results are consistent with previous expectations based on the simple concept of “distorted π-electron clouds”. Facts are presented which indicate that the Δδ_3-1 (or Δδ_3-2) values may serve as empirical measures of the degree of polarization of the π bonds of these fluoroolefins.     

JO2F3, seine Struktur und F-Ionen-Akzeptor-Eigenschaften

IO₂F₃, originally assumed to have a trigonal bipyramidal structure, is polymeric. Mass spectra confirm the existence of molecules with molecular weights up to three times the formula weight. Chemically, IO₂F₃ is a strong Lewis acid and fluorine ion acceptor, thus forming the anion IO₂F₄ ^?. With SbF₅ it forms a further polymeric compound (IO₂F₃·SbF₅) _n .¹⁹F-NMR, mass, IR and Raman spectra confirm the proposed structures.     

Characterization of surface endgroups in polystrene latexes

The stability against electrolytes for all-sulfate, all-carboxyl, and all-hydroxyl, polystyrene model latexes followed the order, sulfate > carboxyl > hydroxyl when determined from an IR light scattering technique. Two types of hydroxyl endgroups were identified by ¹³C-NMR (chemical shift correlations, and model compound comparisons), for the polystyrene model latexes. One type was due to termination of growing chain with an oligomer with a single monomer unit, and the other due to termination of growing chains. The surface hydroxyl groups of an all-hydroxyl latex were derivatized with hexafluoroacetone, and quantified using ¹⁹F-NMR techniques. Good agreement with the indirect conductometric titration values were obtained.     

19F-Labeled Probes for Recognition-Enabled Chromatographic 19F NMR

The NMR technique is among the most powerful analytical methods for molecular structural elucidation, process monitoring, and mechanistic investigations; however, the direct analysis of complex real-world samples is often hampered by crowded NMR spectra that are difficult to interpret. The combination of fluorine chemistry and supramolecular interactions leads to a unique detection method named recognition-enabled chromatographic (REC) ¹⁹F NMR, where interactions between analytes and ¹⁹F-labeled probes are transduced into chromatogram-like ¹⁹F NMR signals of discrete chemical shifts. In this account, we summarize our endeavor to develop novel ¹⁹F-labeled probes tailored for separation-free multicomponent analysis. The strategies to achieve chiral discrimination, sensitivity enhancement, and automated analyte identification will be covered. The account will also provide a detailed discussion of the underlying principles for the design of molecular probes for REC ¹⁹F NMR where appropriate.     

1H,13C and19FNMR studies on the structure of the intramolecularly hydrogen bondedcis-enols of 2-trifluoroacetylcycloalkanones

Summary The¹H,¹³C and¹⁹F NMR spectra of some 2-trifluoroacetylcycloalkanones comprising five-, six-, seven-, and eight-membered ring systems have been studied. These systems have been shown by¹⁹F NMR spectroscopy to be over 90% enolized. The effects of ring size on the¹H,¹³C and¹⁹F chemical shifts and¹³C-¹⁹F coupling constants are discussed. The direction of enolization in these systems was investigated by¹H,¹³C and¹⁹F NMR spectroscopy and evidences were presented in favour of a dominant exocyclic enol form in the five- and an endocyclic enol form in the six-, seven- and eight-membered ring systems.

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¹H-,¹³C- und¹⁹F-NMR-Untersuchungen zur Struktur der intramolekularen Wasserstoffbindung in dencis-Enolen von 2-Trifluoracetylcycloalkanonen

Zusammenfassung Die¹H-,¹³C- und¹⁹F-NMR-Spektren einiger 2-Trifluoracetylcycloalkanone mit fünf-, sechs-, sieben- und achtgliedrigen Ringsystemen wurden untersucht. Mittels¹⁹F-NMR konnte über 90% Enolisierung nachgewiesen werden. Der Effekt der Ringgröße auf die chemischen Verschiebungen in den¹H-,¹³C- und¹⁹F-NMR-Spektren und auf die¹³C-¹⁹F-Kopplungskonstanten werden diskutiert. Die Enolisierungsrichtung dieser Systeme wurde unter Einsatz der NMR-Spektren untersucht: dabei ergab sich eine dominierende exocyclische Enolform für die Fünfringe und eine endocyclische Enolform für die sechs-, sieben- und achtgliedrigen Ringe.

     

Quantitative Analysis of Enzyme-Mediated Hydrolytic Processes and Their Products Using HPLC and NMR Techniques

Second derivatives of the UV spectra of 2-(4-alkoxybenzyl)cyclopentan-1-ols and their acetates were used for the quantitative analysis of reaction kinetics of enzyme-mediated hydrolytic process. To determine the enantiomeric purity of the products using non-chiral HPLC columns, their diastereoisomeric esters of 3,3,3-trifluoro-2-methoxy-2-phenylpropanoic acid(MTPA) were prepared. The absolute configuration of the products was established using a combination of the results of a HPLC analysis and ¹H/¹⁹F-NMR measurements of the diastereoisomeric MTP esters. The analytical method described consists of an easy routine HPLC analysis which can sometimes be used as a quick on-line analysis of the reaction kinetics and as a quick stepwise analysis of the optical purity and the absolute configuration of the products.     

Exposing the Origins of Irreproducibility in Fluorine NMR Spectroscopy

Fluorine chemistry has taken a pivotal role in chemical reaction discovery, drug development, and chemical biology. NMR spectroscopy, arguably the most important technique for the characterization of fluorinated compounds, is rife with highly inconsistent referencing of fluorine NMR chemical shifts, producing deviations larger than 1 ppm. Herein, we provide unprecedented evidence that both spectrometer design and the current unified scale system underpinning the calibration of heteronuclear NMR spectra have unintentionally led to widespread variation in the standardization of ¹⁹F NMR spectral data. We demonstrate that internal referencing provides the most robust, practical, and reproducible method whereby chemical shifts can be consistently measured and confirmed between institutions to less than 30 ppb deviation. Finally, we provide a comprehensive table of appropriately calibrated chemical shifts of reference compounds that will serve to calibrate ¹⁹F spectra correctly.     

Synthesis of (2-p-fluorophenylalanine)oxytocin and its desamino analogue using the S-acetamidomethyl protecting group

[2-p-Fluorophenylalanine]oxytocin ( 1a ), desamino-[2-p-fluorophenylalanine]oxytocin ( 1b ), and desamino-oxytocin ( 2 ) have been synthesised via intermediates containing S-acetamidomethyl-cysteine. The protected linear peptides were built up using both stepwise and fragment-condensation procedures, and the S-protecting groups were removed by iodine with simultaneous formation of the disulfide bridge. The uterotonic activities in vitro of the analogues have been determined. The close similarity of the ¹⁹F-NMR. spectra indicates that the p-fluorbenzyl side chain is freely exposed to the solvent in the disulfide-bridged hormone analogues as well as in their S-protected, acyclic precursors.     

Chalkogenfluoride in niedrigen Oxydationsstufen. IV. Darstellung und Charakterisierung von reinem S2F4

Lower Chalcogen Fluorides. IV. Preparation and Characterization of Pure S₂F₄ Reactions of S and COS, respectively, with elemental fluorine in a metal high vacuum apparatus give a mixture of SF₆, SF₄, S?SF₂, and S₂F₄. At ? 78°C S₂F₄ can be freed from impurities and isolated in a pure state. Molecular weight, density, melting point, vapour pressure, boiling point, IR, UV-, ¹⁹F-NMR, and mass spectra are presented.     

Synthesis and structure of BIS(Trifluoromethyl)BIS(Tri-methylsilyl)Amino dichloroarsorane, (CF3)2AsCl2N(SiMe3)2

The synthesis of (CF₃)₂AsCl₂N(SiMe₃)₂ is reported. This compound has been characterized on the basis of an X-ray analysis. It has a trigonal bipyramidal geometry with axial chlorine atoms. Variable temperature ¹H- and ¹⁹F-NMR data show no observable changes. In comparison to pentacoordinated phosphorus compounds the tendency to form tetracoordinated derivatives is strongly diminished in the case of arsenic compounds.